This invention relates to measuring devices for measuring of an object under test, e.g., a baggage sorting system, a printed circuit board inspection system, or any device for measuring dimensions or other characteristics of objects based on transmission or reflection of light.
FIG. 2 shows the arrangement of a conventional measuring device. In this device, a laser beam emitted from a light source 1 such as a semiconductor laser is applied to a rotary polygonal mirror 2 forming a scanning section, where it is reflected. The rotary polygonal mirror 2 is rotated by a motor (not shown) or the like, so that the direction of reflection of the laser beam is changed over a certain range of angles (.theta.). This causes the beam to be swung in a plane parallel to the surface of the drawing at a certain speed, so that scanning with the laser beam is carried out.
The scanning laser beam is applied to a lens 3 consisting of a convex lens or an f.theta. lens. The rotary polygonal mirror 2 is positioned at the focal point of the lens 3, and therefore rays of light emerging from the lens 3 are in parallel with one another irrespective of their scanning positions. The laser beam emerging from the lens 3 is applied to a convex lens 4, so that it is focused on a photodetector 5.
An object 7 under test is positioned between the lens 3 and the convex lens 4, so that a part of the laser beam is blocked by the object 7 and is not applied to the photodetector 5. Hence, by measuring the time for which the output level of the photodetector is decreased, the vertical length (in FIG. 2) of the object 7 can be determined.
A problem with a device of this type is that the use of the convex lens 4 to focus the light on a single photo sensor makes the device bulky and increases the manufacturing cost, and further it is difficult to perform measurements with high accuracy because of the aberration of the convex lens 4.
In a conventional baggage handling system, a scanning beam is typically not used, but instead the light source is a beam of predetermined width. Rather than using a convex lens and a single photodetector, the light receiving section is a photodetector array made up of a number of photodetectors arranged in a straight vertical line. As the baggage is conveyed between the light source and photodetector array, the quantity of light intercepted corresponds to the size of the baggage.
Even in this case, however, the measuring device is not only intricate in construction, because it includes the wiring, but is also high in manufacturing cost.
The present invention also relates to an inspecting apparatus for inspecting foreign matters attached to an iron plate, a film, etc., or for detecting defects thereof and positions, dimensions, etc., of parts arranged on a substrate. FIG. 9 shows the construction of a conventional inspecting apparatus as an example. In this figure, reference numeral 61 is an object to be inspected such as an iron plate, a film, etc., and reference numeral 62 is a photodetector array in which a plurality of photodetectors are linearly arranged.
An object 61 is irradiated with a laser beam and the reflected light is detected by photodetector array 62. When foreign matters such as dust, dirt, etc., are attached to object 61, or when there are defects such as flaws, cracks, etc., on object 61, the amount of reflected light from the dirty or defective portion is different from the amount of light reflected from the normal portion. Accordingly, the object can be inspected by this change in the amount of light. The inspected object is scanned by the laser beam in the direction of arrow A in FIG. 9 and is moved in the direction of arrow B. Thus, the entire object 61 can be inspected.
However, in such a conventional apparatus by using photodetector array 62, the wiring processing with respect to the individual photodetectors becomes complicated and the apparatus becomes large as the length of the array becomes long. Further, there are variations in characteristics, and a dead band, i.e., a region of insensitivity, may exist between adjacent photodetectors. Accordingly, it is necessary to arrange the respective light-receiving elements such that the adjacent photodetectors partially overlap each other, or arrange a diffusion plate in front of the photodetectors. Thus, it is difficult to perform an accurate and fine inspection, and the apparatus becomes complicated and expensive.
Further relating to printed circuit boards, there are various kinds of design rules regarding the width of a conductive portion (pattern), the interval between the conductive portions, land diameter, etc. A printed circuit board detecting apparatus of the type shown in FIG. 9 may be used to detect whether or not a printed circuit board having a predetermined pattern thereon meets these design rules. To inspect the printed circuit board, it is scanned by a laser beam and the reflected light is received by a photodetector array in which a plurality of photodetectors are linearly arranged. The conductive portion which is made of copper, etc. and a base material portion which is made of glass. epoxy resin, etc., are different from each other in the directivity of the reflected light. Normally, the conductive portion is higher in reflectance than the base material portion, so that it detects a larger amount of the reflected light. Accordingly, the pattern of the printed circuit board can be inspected from the change in output of the photodetector array. It is also known to have the reflected light at each scanning position incident onto a single photodetector by way of a condenser lens arranged in front of this single photodetector.
The design rule inspection apparatus using a detector array suffers from the same problems discussed above with respect to the flaw detection apparatus. For the design rule inspection apparatus which uses a condenser lens to converge the reflected light onto one photodetector, it is necessary to employ a large-sized condenser lens to scan at once a wide range of the printed circuit board. Hence, the apparatus becomes large and expensive.
In view of the foregoing, an object of this invention is to provide a measuring device which is small in size and low in manufacturing cost, and permits measurement with high accuracy.
It is a further object of the invention to provide a compact and inexpensive object inspection system which can perform an accurate and fine inspection at once over a wider range of an object.